1. Field of Industrial Application
This invention relates to methods to produce solid electrolyte composites and solid electrode composites employed extensively to fabricate solid electrochemical products such as batteries, capacitors, sensors, display devices, recording devices, etc. More specifically, this invention relates to methods to attain uniform solid electrolyte composites and solid electrode composites by adding a specific surfactant to a slurry in which an elastomer is dispersed or dissolved and solid electrolyte powders and/or electrode active material powders are dispersed or dissolved without causing coagulation of said solid electrolyte powders.
2. Prior Arts
It had been known that electrochemical devices, such as compact and thin batteries, electrical double layer capacitors, etc., can be constructed, without leakage of liquid electrolyte, by employing solid electrolyte. However, since such devices employing solid electrolyte lack mechanical elasticity, they are brittle or highly vulnerable against mechanical shocks.
To solve such problems, one method was disclosed in Japanese Laid-Open Patent No. 63-245871 where flexible electrochemical devices resistant to mechanical shocks were fabricated by mixing solid electrolyte powders and/or electrode powders with elastomer such as synthetic rubber; i.e., the electrolyte powders or electrode powders are mixed with an insulating plastic resin to form a practical solid electrolyte composite or electrode composite.
Said solid electrolyte composite or electrode composite made of a plastic resin and solid electrolyte powders or electrode active material powders is produced by dispersing solid electrolyte powders and/or electrode active material powders in plastic resin. That is, these powders are dispersed into a solvent in which plastic resin is dissolved in order to form a slurry firstly; the solvent is removed during or after a molding process involving that slurry.
In these processes, a lipophilic nonpolar solvent such as toluene is employed because solid electrolyte powders are ionic in nature and are slightly dissolved and denatured in a hydrophilic solvent or polar solvent such as water, alcohol, and acetone.
Because solid electrolyte powders are hydrophilic, they are easy to coagulate in a lipophilic solvent to form secondary particles, which unevenly disperse in plastic resin. Moreover, in order to maintain a sufficient ionic conductivity of electrolyte, the amount of plastic resin mixed should be minimized. Thus, it had been very difficult to produce a uniform solid electrolyte with higher mechanical strength, particularly in a product involving large area.
Furthermore, in the production of electrode composites where electrolyte powders and electrode active material powders are mixed with or dispersed in a plastic resin, said solid electrolyte powders form secondary particles. Since these secondary particles are hardly evenly dispersed or admixed in plastic resin, the resultant electrode composite provides a poor ionic conduction when a smaller amount of solid electrolyte powders are admixed in the electrode composite in order to obtain a higher electrode capacity. This resulted in another disadvantage of extremely low electrode utilization.